This invention relates to a suspension control for a wheeled vehicle having a body suspended by suspension springs at a plurality of points on unsprung, road contacting wheels.
The co-pending patent application U.S. Pat. No. 07/430,858, entitled Full Vehicle Suspension Control, filed Nov. 2, 1989 by Kamal N. Majeed and assigned to the assignee of this application, describes a real time, full vehicle suspension control in which the desired force exerted by an actuator between each vehicle wheel and its corner of the vehicle body is derived from an equation which includes the linear, weighted sum of the vehicle body heave, roll and pitch velocities. These velocities are derived from an absolute accelerometer at each body corner mounted to sense the (presumably) vertical absolute acceleration of that corner of the vehicle body. In the system as disclosed in that application, each accelerometer signal is integrated to provide a vertical body corner velocity signal, and the heave, roll and pitch velocities are derived from the four vertical body corner velocity signals by straightforward linear mathematical equations.
However, the accelerometers do not produce purely vertical accelerations at all times. Even if the accelerometers are all perfectly vertically aligned on an unaccelerated vehicle, the vehicle body, which is subject to pitch and roll during vehicle acceleration, braking and cornering, often places these sensors at an angle from the purely vertical. The resulting nominally vertical acceleration signals may thus at times include longitudinal or lateral acceleration components which constitute non-vertical errors. These errors, although quite small, may be greatly increased by integration as the body corner acceleration signals are converted to body corner velocity signals. This tendency is even greater if the accelerometers are not perfectly vertically mounted on the vehicle. In addition, the integrator used for converting acceleration signals to velocity signals is bounded: that is, its output is subject to saturation at a maximum output level. Thus, the non-vertical errors, greatly increased during integration, may hasten the onset of integrator saturation and lead to inaccuracy.